Method of preparing soy

ABSTRACT

A method of preparing soy which is featured in that soybeans obtained by steaming soybeans of a moisture content of 30-70 percent by weight with saturated steam of a gauge pressure not less than 1.8 kg./cm.2 for a short period of time not exceeding 10 minutes, followed by rapid cooling to a temperature not exceeding 100* C. are used as the starting material for the preparation of soy. And the method can provide a soy of superior flavor and of high quality wherein the possibility of the formation of clouds and precipitates when diluted and heated in its use does not occur, and can be carried out industrially advantageously with improved yield and good reproducibility.

United States Patent Yokotsuka et a1.

METHOD OF PREPARING SOY Inventors: Tamotsu Yokotsuka, Higashikatsushikagun; Tatsuo Aonuma, Kashiwa-shi; Koya Mogi; Danji Fukushima; Atsushi Yasuda; Hiroharu Watanabe; Naoshi Tsukada; Akira Arsi, all of Noda-shi, Japan Markley, Klare, Soybeans and Soybean Products Vol. 11 Inter- STEAMING PRESSURE (K GAUGE) Mar. 7, 1972 science Publishers Inc. New York 1951 pp. 991- 997 Primary Examiner-Raymond N. Jones Assistant Examiner-William Andrew Simons Attorney-Wenderoth, Lind & Ponack [57] ABSTRACT A method of preparing soy which is featured in that soybeans obtained by steaming soybeans of a moisture content of 30-70 percent by weight with saturated steam of a gauge pressure not less than 1.8 kgJcm. for a short period of time not exceeding 10 minutes, followed by rapid cooling to a temperature not exceeding 100 C. are used as the starting material for the preparation of soy. And the method can provide a soy of superior flavor and of high quality wherein the possibility of the formation of clouds and precipitates when diluted and heated in its use does not occur, and can be carried out industrially advantageously with improved yield and good reproducibility.

5 Claims, 1 Drawing Figure llllll e 7 s 9 STEAMING TIME (mm) Pmmmm 71912 STEAMING PRESSURE (Kg/CF0 GAUGE) IIIIIl-ll l2345e 891o S'TPIAMING TIME (mm) /NVEN70/?S TAMOTSU YOKOTSUKA TATSUO AONUMA KOYA MOGI DANJI FUKUSHIMA ATSUSHI YASUDA HIROHARU WATANABE NAOSHI TSUKADA AWRA ARI-XI ATTORNEYS METHOD OF PREPARING SOY This invention relates to a method of preparing soy, employing an improved operations of treating the starting soybeans, whereby is obtained a soy of superior flavor and of high quality wherein the possibility of the formation of clouds and precipitates due to the coagulation of protein during dilution and heating does not occur and in which the preparation can be carried out commercially advantageously with improved yield and good reproducibility. More specifically, the invention is characterized in that the soybeans utilized as the starting materials for producing soy are initially steam treated under specific conditions before culturing the soybean in the usual manner.

More particularly, the present invention relates to a method of preparing soy by initially steaming soybeans of a moisture content of 30-70 percent by weight with saturated steam of a gauge pressure not less than 1.8 kg./cm. for a short period of time not exceeding minutes, followed by rapid cooling to a temperature not exceeding 100 C. and using the thus-treated soybeans as the starting material in the conventional culturing technique as described below.

In preparing soy, generally vegetable protein-containing materials and carbohydrates are used as the principal starting materials. These are treated by customary procedures, after which the mixture is inoculated with aspergilli, the solid culture thereof then being carried out under open conditions to make the Koji. A soy mash is prepared from this solid Koji by mixing it with a solution of common salt, which mash is then fermented by the activity of the naturally propagating and/or artificially inoculated micro-organisms, principally soy lactic acid bacteria and soy yeasts. The soy is then obtained by removing the solid portion from the brewed mash.

As the foregoing vegetable protein-containing materials and carbohydrates, soybean and wheat are usually used, it being the usual practice to use these as the soy brewing starting ingredients after steaming the former with saturated steam of a gauge pressure of the order of 0.7-1 .0 kg./cm. (at 1 -1 19 C.) for about -60 minutes and after parching and crushing the latter at normal atmospheric pressure.

It is known that the nitrogen source that can be utilized for the preparation of soy can be increased by the use of soybeans which have been steam treated as hereinabove noted as the starting material for preparing soy. And from long experience soybeans which have been treated at a gauge pressure and for a period of time such as indicated above have been employed as being optimum conditions for the preparation of soy by the brewing method.

While it is not quite clear as to what state of denaturation of the protein is most advantageously utilizable as the nitrogen source during the brewing of soy, it is known that if the steaming treatment for accomplishing the denaturation is insufficient the protein does not readily undergo enzymatic digestion during the preparation of soy. Further, if soy products produced by inadequate steam treatment of soybeans are used, (which soybeans will hereafter occasionally be referred to as native soybeans, and their protein as native protein) is diluted with water and heated in use, the formation of clouds or precipitates cannot be avoided and thus its commercial value as soy is lost. On the other hand, in the case of soybeans which have been denatured to an excessive degree (hereinafter may, at times, be referred to as secondarily denatured soybeans, or its protein as secondarily denatured protein), the rate of digestion of the nitrogen source by means of enzymes declines during the preparation of soy, with the consequence that the yield of soy suffers. Since soy is produced on a large scale, even a few percent decline in yield directly affects the product cost.

Therefore, it is of great importance that soybeans denatured to the optimum state be used in preparing soy by the brewing technique, for not only maintaining the quality of the product which meets that required of soy but also for improving the yield of the product. In the past, a steaming treatment with saturated steam of the order of 0.7-1.0 kg./cm. gauge (at a temperature [IS-119 C.) for about 30-60 minutes was regarded as being the optimum. The rate of digestion of the proteinanceous nitrogen source of soybeans by means of enzymes that could be achieved in the past by the brewing technique using soybeans which have been steam treated as described was of the order of -85 percent, and about 87 percent at most, when indicated by the-method of indication hereinafter fully described.

The optimum steaming conditions such as set forth above, which were used in the past, were attained empirically in the art of brewing soy over a long period of time, it being known from experience that in the case of soybeans treated at gauge pressures and treatment times less than those indicated the product soy would contain more or less of the native protein in a relatively high proportion which resulted in the formation of the aforementioned clouds and precipitates when diluted and heated, making the product less commercially valuable other hand, it was known that under conditions exceeding such formerly used gauge pressures and treatment times, the presence in the product soy of secondarily denatured protein in a relatively high proportion resulted in the decline in the rate of digestion of the protein of the material soybeans by means of the enzymes thus bringing about a decline in the yield of the product soy.

With a view to providing a method of advantageously preparing soy by the brewing technique by employment of a more advantageous steaming treatment of the starting materials and in which not only an improvement is had in the yield of the product soy but also the soy so produced is one in which there is no possibility of the formation of clouds or precipitates when being diluted and heated in its use, we made a detailed study of the relationships between the moisture content of the soybean, the gauge pressure of the saturated steam used for the steaming treatment, and the steaming time. As result, we found that there existed an intimate relationship between these three factors.

We further found that by combining the conditions of l) the use of saturated steam of high gauge pressure (hence elevated temperature) (by which use it was heretofore expected that a major portion of the protein of the material soybean would naturally undergo secondary denaturation to cause a decline in product yield), (2) a short-treatment time (by which use it was heretofore regarded that a major portion of the protein of the material soybeans would naturally remain native to cause a loss of the commercial value of the product soy), and (3) quick cooling of the material soybeans to not over l00 C. after the steaming treatment; contrary to expectations and the optimum conditions that have been established after long experience in the art of preparing soy, soy of excellent quality could be provided industrially advantageously by the brewing technique by means of an improved short period steaming operation of the material soybeans and with an improvement in the yield of the product soy.

It is therefore an object of the present invention to provide a method of preparing soy of superior flavor and of high quality wherein the possibility of the formation of clouds and precipitates when diluted and heated in its use does not occur, and in which the preparation can be carried out industrially advantageously with improved yield and good reproducibility.

Other objects and advantages of this invention will become apparent from the following description.

According to the invention method, in carrying out the conventional method of preparing soy by brewing the starting ingredients for preparing soy, including soybeans, using the soy preparing fungi, as said soybeans are used those whose moisture content is 30-70 percent by weight, which have been steam treated by saturated steam of a gauge pressure not less than 1.8 kg./cm. (13l C. at l.8 kg./cm. for a short period of time not exceeding 10 minutes, followed by quickly cooling to a temperature not exceeding C.

For facilitating an understanding of this point, the accompanying drawing, which is a graph illustrating roughly the interrelation of the moisture content of the soybeans and the steam pressure (gauge) of the saturated steam used and the steaming time, will be referred to.

More specifically, the FIGURE is a graph illustrating roughly the relation between the steam pressure (gauge) of the saturated steam used and the steaming time in case the moisture content of the soybeans is 60 percent by weight.

In the FIGURE, the curve a indicates the boundary of the degree of denaturation of the material soybeans which separates the soy in which is formed clouds and precipitates to an extent as to be given the hereinafter described turbidity grade" of l or more, and the soy of a turbidity gradeof in which no clouds or precipitates are formed. The zone at the left side of curve a in this FIGURE is that where a great proportion of the protein of the soybean remains native and hence the commercial value of the product as'soy is lost. On

the other hand, the curve b in the FIGURE indicates by means of the hereinafter described rate of digestion the boundary beyond which the yield of the product soy becomes worse because of the large proportion of the secondarily denatured protein in the soybeans. This FIGURE shows that for achieving the commercially satisfactory improvements in the various points as contemplated by the present invention the conditions for steam treating the soybeans must be chosen from those falling within the scope indicated by the hatching in the FIGURE.

This hatch-indicated scope is also influenced by the moisture content of the soybeans as well as their form, but the most important factor is the moisture content. When the moisture content is on the higher side of the aforesaid 30-70 percent by weight range, this scope tends to shift in the left direction of the FIGURE with curves a and b rising more abruptly. On the other hand, when the moisture content is on the lower side of the foregoing range, the tendency is for the scope to shift in the right direction in the FIGURE with these curves rising more gently.

The soybeans to be steam treated in accordance with the invention may be of any form that is usually used as the starting material for preparing soy, such as whole soybean, soybean flour, defatted soybean flake, or soybean meal, there being no particular restrictions so long as they contain soybean protein which can become the source of nitrogen. In the case of whole soybeans, those whose moisture content is of the order of 30-65 percent, and particularly 55-60 percent by weight, are to be preferred. On the other hand, in the case of those of other form, preferred are those of a moisture content of 45-70 percent, and particularly 55-65 percent by weight.

For bringing the moisture content up to these levels, the beans are either soaked in water or added the water by sprinkling, spraying or any other suitable means. If the moisture content is less than that indicated by the foregoing ranges, the proportion of the protein remaining native in the soybeans after steaming becomes such that it causes a loss in the commercial value of the product soy. For example, the dried whole soybean that is usually available has a moisture content of about percent by weight. Now, if such dried soybean is given a steaming treatment without increasing its moisture content, even though it has been given a steaming treatment for about 3 hours, the soy product forms clouds or precipitates upon dilution, and heating, which phenomena is caused by the presence of native protein in the soybean. 0n the other hand, the employment of a moisture content in excess of the foregoing range makes it difficult to carry out either the steam treatment operation itself or the subsequent Koji-making steps.

The steaming treatment is carried out with saturated steam of a gauge pressure not less than 1.8 kg./cm. On the other hand, the steaming time employed (which is the period of time after the prescribed pressure of not less than 1.8 kg./cm. has been reached) is a short period of time not exceeding 10 minutes. In general, when the gauge pressure is high, a relatively short period of time is employed, whereas when the gauge pressure is a low value close to the aforesaid L8 kg./cm., a time preferably close to ID minutes is used. A pressure ranging between 1.8 and I5 kg./cm. gauge is usually chosen, but preferred is a pressure 2.0-9.0 kgjcm. gauge and especially recommended is a pressure 4-7 kg./cm. gauge. As

the gauge pressure is increased, the treatment time is correspondingly shortened suitably. For example, at a pressure of 3 kg./cm. gauge, a treatment time of the order of 2-4 minutes is employed, whereas at a pressure of 5 l g./cm. gauge, a shortened time of the order of 30 seconds to 2 minutes is suitable. However, a short treatment time of such, say, as one-half second, which is operationally difficult of being practiced should preferably be avoided. Needless to say, in an apparatus wherein the steaming operation is carried out by placing thin layers of the soybeans on grated plates in multistage fashion, a short-steaming treatment of such as a few seconds can also be employed. Normally, it is, however, preferred that the gauge pressure of the saturated steam is so chosen that the treatment time becomes from about I second to 10 minutes, and preferably from about 15 seconds to 6 minutes.

Thus, the time for the steaming treatment can be reduced to less than one-third of that of the conventional method, for example, even as much as less than one-thirtieth, with the consequence that great advantages are had in connection with the steam treatment operation of the material soybeans.

When the soybeans to be used as starting material are those which have been treated in accordance with the present invention with higher gauge pressures (and hence at elevated temperature) and shorter treatment times than the steaming conditions which were heretofore recommended, the denaturation of the protein contained in the soybeans becomes such that it is most suitable for the purpose of soy brewing. In this case, as soon as the steaming treatment has been completed, the treated soybeans must be cooled as quickly as possible to a temperature not exceeding C. While the cooling time will vary depending upon the gauge pressure at which the treatment is carried out, in general, it is preferred that the reduction to a temperature not exceeding l00 C. be carried out at shorter periods of time in the case of higher gauge pressures. For example, in the case where the gauge pressure does not exceed 3 kg./cm. (l43 C.) the temperature of the treated soybeans should be reduced to below 100 C. within at most 15 minutes, and preferably within 5 minutes. On the other hand, when the pressure exceeds 3 kg./cm.- the reduction of the temperature to below 100 C. should be accomplished within at most 5 minutes, and preferably within l minute. Thereafter, the temperature preferably should be cooled to the neighborhood of 40 C. as promptly as possible. This is because the protein, which, as a result of its treatment at an elevated temperature for a short period of time, has become readily susceptible to digestion by enzymes, is more sensitive to heat than the protein which has received the conventional treatment, with the consequence that the progress of secondary denaturation is apt to take place and rather render the rate of enzymatic digestion of the protein worse than that of the conventional method. Hence, the slow cooling of the soybeans after completion of its steaming greatly reduces the effects of the present invention.

The cooling can be accomplished by withdrawing the soybeans from the steaming zone and spreading them out and allowing them to cool by exposure to air, at which time air can be positively blown against the soybeans. This air can be cooled air. Alternatively, quick cooling can be carried out by employment of a reduced pressure means such as a jet condenser or a vacuum pump and evaporating the moisture content of the treatment-completed soybeans which are in the steaming zone or have been removed therefrom, thus utilizing the latent heat of the moisture which is evaporated to accomplish the cooling. A still another very effective means of achieving the objective of the present invention is to discharge the streaming treatment-completed soybeans from the pressure treatment vessel filled with the saturated steam instantaneously to air of normal pressure or to a low-pressure environment of a pressure close to that of normal atmospheric pressure to effect the sudden cooling of the soybeans by the so-called puffing phenomenon.

An illustration is presented in Table l, below showing the different rates at which the proteins are digested by means of the enzymes produced by the fungi which are typically used in the brewing of soy in the several cases of the soybeans treated in accordance with the invention method, the soybeans which have undergone treatment at conditions in which either the activity of proteinase which forms 1 'y of tyrosine per minute when the enzymatic reaction is carried out at 30 and pH=7.2 using as the substrate 1% milk casein.

gauge pressure or treatment time does not satisfy the require- 5 Measurement f T bidi G d ments of e Present lhvehtlehi and Soybeans treated After having conducted the enzymatic digestion in ach With the heretofore recommended and Ptaetteed cordance with the method of measuring the rate of digestion eehdltlohsas hereinbefore described, in adding the distilled water to the I The Values of the fate of thgesttoh and tutbtdlty grade used digestion liquid to make its total volume l00 ml. instead of the In the table were measured the following manner, and the m distilled water an aqueous NaCl solution is used, which is greater h value of the rate of digestion; the m suitable is added such that the NaCl concentration in the total solution the erotelheehatuted e the Purpose of btewthg Yr hence becomes 1.8-2.0 percent. Next, a centrifuge is employed, and also mdleatlhg that the yield of the Product 1S hlgh- Oh the the liquid and solid phases are separated. Half of the liquid other h e 35 t0 the tut'bldtty grade. a value of grade 1 15 phase portion is heated at 100C. for 5 minutes, while the unhtghet mttleates that 35 the Product ts one of P of he heated other half is used as control. The two are then commmer i l l ince clouds and precipitates are formed pared with the unaided eye and the turbidity grade is deterdurmg its dllutl n and h atmgmined in accordance with the following standard: Method of Measuring the Rate of Digestion Soybeans whose steaming treatment has been completed 20 Clouds formed 1 are vacuum dried at a low temperature and the comminuted. Pmipimes formed 2 One gram of the powdered specimen is placed in a shaking- No discernible formation Ofclouds o TABLEl Steaming treatment Gauge pressure. Time kg./cm. required Rate of Tur- (temperature Treatment to cool digestion bidity Experiment 0.) time to 100 C. (percent) grade Conventional method..... 0.9 (117) 45 minutes. 20 minutes. 86.13 0 Comparison 1.... I. 2 (123) minutes.. 10 minutes" 81. 05 2 Present invention 1.8 (131) 8 minutes..- 3minutcs 91.40 0 Comparison 2.. 1.8 (131) minutes ..do.. 80. 23 0 Present invention 2. 0 (133) 5 minutes .d0 91. 60 (1 2.0 (133) .do minutes.. 83.50 0 3.0 (143) 3 minutes... 3 minutes.. 92. 99 0 4. 0 (152) 2minutos... 1 niinute 93. 74 0 5.0 (159) 1 minute. 40 seconds 94. 50 O 6.0 (165) seconds ..do.. 94.90 0 7.0 (170) 15 seconds do.. 95.10 0

No'rE.-Soybean used was defatted soybean fiakc of a moisture content of 60% by weight.

type test tube, to which are then added 10 ml. of 0.5 mol phosphoric acid buffer solution (pH=7.2), 20 ml. of an en- 40 zyme solution (see note) and 1 ml. of toluol, after which the test tube is tightly stoppered. The enzymatic digestion is then carried out by maintaining the temperature of this test tube at 37 C. for l68 hours (7 days) while gently shaking the tube.

After completion of the above-described digestion, distilled water is added to the digestion liquid to make the total quantity 100 ml. This is followed by using a centrifuge and separating the liquid and solid phases. Taking 30 ml. of this liquid phase portion, 15 ml. of 1.2 mol trichloroacetic acid are added thereto, whereupon the undigested protein precipitates. After filtering off this precipitate, the nitrogen content in 5 ml. of the filtrate is measured in accordance with the Kjeldahi method. Separately, a blank test is conducted in similar manner but without adding the foregoing powdered specimen 5 5 BO-{L-lti 1%) Rate of digestion B X 100 AX 3O X 100 NoTE.The aforesaid enzyme solution denotes an extraction solution extracted from a solid K911 of wheat bran obtained by using Aspergillt s 8010.6, a typicalfungus used for brewing soy, and having a proteinase activity of 53[PU]i-,f 'lml. 1[PU]$L;,"- '/m1. as here used, represents the As apparent from the results given in Table l, above, it is possible according to the present invention to choose the gauge pressure, steaming time and the time to cool to a temperature not exceeding C. so that the rate of digestion in the present invention, excepting that soybeans which 7 have been steam treated as hereinbefore fully described are used as the starting material, the preparation of soy is otherwise carried out in accordance with the brewing technique well known in the art. That is to say, parched and crushed wheat is added to the soybeans which have received the steaming treatment in accordance with the invention method, as hereinbefore described, and the two are mixed together. The mixture is then inoculated with aspcrgilli and by carrying out the solid culture at 23-35 C. for 40-90 hours Koji is obtained.

Next, a soy mash (moromi) is prepared from this solid Koji by mixing it with a solution of common salt. This mash is stored for 4-18 months in storage tanks until fully matured. During this period the mash is fermented by the activity of the naturally propagating and/or artificially inoculated micro-organisms, principally soy lactic acid bacteria and soy yeasts. The matured mash is separated into filtrate (unpasteurized soy) and cake by pressing. Refined soy is obtained by heating this filtrate to pasteurize it.

The aspcrgilli here used are those aspcrgilli known in the soy brewing art and can be freely chosen and used. As such aspcrgilli, those which are used most commonly are the fungi of the genus Apergillus, particularly the yellow Aspergilli, while those referred to as conidia heads are green, blue-green or yellow and are fungi which do not form perithecia and ascospores [the classification in Thom & Raper, Manual of the Aspergilli" (1945, William 8L Wilkins)]. Specifically, the following groups can be named:

l. Aspergillusflavus-oryzae group, 2. Aspergillus ochraceus group, and 3. Aspergillus tamarii group. As examples of fungi belonging to the aforesaid Aspergillus Ninety-nine kilograms of defatted soybean flakes sprinkled with 129 liters of water (moisture content 60.9 percent were continuously introduced into a steaming kettle of saturated steam pressure of 7.0 kg./cm. gauge, held in residence therein flavus-oryzae gro p, included r Aspe gil us yz e, spergi 5 for 15 seconds and thereafter continuously discharged into air Ills $01118, Aspergillus Oryzae fl 1 8 to be cooled rapidly, thereby obtaining steamed defatted Y magnaspomsv As examples 0f those belonging soybean flakes whose temperature was 40 C. one minute to the Aspergillus achraceus group, included are Aspergillus lateh ochraceus, Aspergillus melleus, Aspergillus oniki, etc. And as steaming Treatment fs b (ii) examples of those belonging to the Aspergillus ramarii group, 10 Ninety-nine kilograms of defatted soybean flakes sprinkled lhcludhd are Aspergillus However Sakaguchl with 129 liters of water (moisture content 60.9 percent) were Yamaha Chem- 9 65 (1944)) steamed for 2 minutes in a steaming kettle of saturated steam ferem'ate thesehy ma f"Y classlficatlon: pressure of 4 kg./cm. gauge, after which the pressure of the I The ergluus some i h has formed kettle was reduced to normal atmospheric pressure in l on comma and whose Fomdlophore wan Smooth 15 minute, thus reducing the temperature of the defatted soybean That of the Asperglnusflavus'oryzae h f much does flakes to below 100" C. This was followed by jetting presh a small projecnon on comma and whose surized water into a jet condenser connected to the steaming comdlophore wan ls rough kettle to thereby accomplish the rapid suction of the steam in- Howeveri Since Thom Rape holds that Aspergiuus sojae side the steaming kettle and the moisture content of the longs to group we wish to add that the fungi 2O steamed defatted soybean flakes. Thus was obtained defatted to be used in this invention comprehends any and all of those Soybean flakes having a eemperature f C in accordance with any of the foregoing classifications. Steaming Treatment of soybeans (iii) The soy lactic acid bacteria and soy yeasts used in the fer- Ninety-nine kilograms of defatted soybean flakes sprinkled mentation step are tho e micro-organisms which are known in with l29 liters of water (moisture content 60.9 percent were th an f soy preparation, Th l ti a id b t ria may b steamed for 5 minutes in a steaming kettle with saturated any which range from those which are salt tolerant to halophilt am 0f 2 kg./cm. gauge pressu after which the Pressure ic and anaerobic to microaerophilic, which can form lactic inside the kettle was reduced to normal atmospheric P acid and can assist the growth f the yeasts and ripen the Soy in 40 seconds to thus reduce the temperature of the defatted aroma and flavor. Included are, for example, Pediacoccus, 30 Soybean flakes below Immediately thereafter the Momma-"us, Streptococcus Tetmmccus, eta Depending steamed defatted soybean flakes were taken out from the upon the lactic acid bacteria, there are some which perform sthammg kettle ahdfspread 9 h a layer of Several cehhmetel' homofermemation while there are some which perform th ckness atop a wire netting-like belt conveyor. While the heterofermemation Either can be used layer of steam-treated defatted soybeanflakes was conveyed One of the bacteria most commonly used in brewing soy is along on thls i was passed rahldly exemplified by Pediococcus soyae. According to the classificathrong}; s layer at a a location Thus was l, tion of Nakagawa & Kitahara (J. Gen. Application Microbiol. 2 efaned Soybean akes havmg a temperature of 40 5 95 957)) sald l' soyae held to be a variety Steamed defatted soybean flakes obtained by the foregoing of Pedzococcus halophzlus MEES 1934). 40

treatments (I) (Ill) in amounts of 99 kg. (calculated as the Further h yeasts Such as noted i? are also amount before treatment) were used, to which were added 94 know m the These h F possess osmophlhc Proper kg. of parched and crushed wheat. These mixtures were then are salt tolerant or halophlhc and usually Possess Sugar inoculated a strain of Aspergills soyae and the solid culture was tolerance. Preferably it is those which can carry out fermentacarried out at for 70 hours to obtain Koji following tion of such as alcohol in the presence of above 15 percent of which 3 0 liters f 24 5 percent by weight brine were added common Salt There are those of these yeasts which belong to and the mixtures were stored and fully matured for 120 days at ehhel' the family Ehdomycemceae the family Cryptococ' 2830 C. On the other hand, as starting material treated in (136638 in accordance With the Classification of Yeasts, in accordance with the conventional method, 99 kg. of defatted Roddel' & KY 8 l Yeasts A Taxonomic soybean'flakessprinkled with I29 'liters of water (moisture Examples Of those belonging to Ehdomycetaceae include Such content 60.9 percent) and thereafter steamed for 45 minutes as Saccharomyces rouxii and Saceharomyces acidifaciens. with aturat d team of a ga ge pre ure of 0,9 kgjcm. were Saceharomyces rouxii comprehends those micro-organisms used, and under identical conditions as hereinbefore which are referred to as Zygosaccharomycer soyae, described the so obtained steamed defatted soybean flakes Zygosaccharomyces major, Zygosaccharomyces sulsus, etc., 5 5 were made into Koji, added the brine and'stored and fully maand osmophilic Zygosaccharomyces. Those belonging to tured. The results of a comparison of the so obtained soys as to Cryptococcaceae include the genus Tolulopsis yeasts such as their composition are shown in Table II.

TABLE II Percent Com- Total Nitrogen Turnion nitroin amino Yield of Rate of bidity Example salt gen form nitrogen digestion grade Conventional method 17. 40 1.653 0. 817 82.05 86.13 0 Exam 1e:

1 treatment (i)] 17.40 1.778 0.878 88. 26 95.10 0

2 [treatment (ii)] 17. 40 1. 752 0.839 86.87 93. 74 0 3 [treatment (iii)] 17. 4.0 1. 697 0.837 84. 24 91. 0

Tolulopsis versatilis, Tolulopsis sphaerica, Tolulopsis sake, Tolulopsis halophilus, etc. These yeasts may be used either singly or in combination according to this invention.

The following examples are given for illustrating one mode of practicing the present invention.

EXAMPLES 1-3 Steaming Treatment of Soybeans (i) EXAMPLE 4 129 kg. of whole soybeans were soaked in cold water for hours and drained of the water for 1 hour (moisture content 58 percent). These soybeans were introduced into a treatment kettle containing saturated steam of 6 kg./cm." gauge pressure and were held therein for 40 seconds, after which they were suddenly discharged into air and cooled. Ninety-four kilograms of parched and crushed wheat were added to the so treated soybeans and, after being inoculated with Aspergillus sayae, the solid culture of the mixture was carried out at 33 C. for 70 hours to obtain Koji. Three hundred and sixty Liters of 24.5 percent brine were then added to the so obtained Koji, and the mixture was stored and fully matured at C. for 120 days to obtain a soy mash of good flavor. The rate of digestion was 92.85 percent, the turbidity grade was 0, and the yield of nitrogen was 85.34 percent.

EXAMPLE 5 denly discharged into air to obtain a cooled mixture of the whole soybeans and defatted soybean flakes. Ninety-four kilograms of parched and crushed wheat were mixed with the foregoing mixture, and thereafter as in Example 4 the Koji was prepared, the brine was added and the resulting soy mash was stored and fully matured at 28 C. for 180 days to obtain a soy mash of good flavor. The rate of digestion was 93.01 percent, the turbidity grade was 0, and the yield of nitrogen was 86.18 percent.

1. We claim:

1. 1n the method of preparing soy by steaming soybeans, mixing the steamed soybeans principally with carbohydrates as the starting materials, inoculating this mixture with aspergilli, culturing the mixture to form solid Koji, adding a solution of common salt to form a soy mash and removing the solid portion from the brew mash thus-obtained, the improvement wherein the initial steam treatment is carried out by steaming soybeans of a moisture content of 30-70 percent by weight in the presence of saturated steam of a gauge pressure not less than 1.8 kilograms per square centimeter for a time not exceeding 10 minutes, followed by quickly cooling the steamed soybeans to a temperature not exceeding 100 C.

2. The method according to claim 1, wherein the steaming is completed so that the rate of digestion of the soybeans becomes not less than percent and the turbidity grade thereof is zero.

3. The method according to claim 1 wherein said gauge pressure ranges between 2 kilograms per square centimeter and 15 kilograms per square centimeter.

4. The method according to claim 1 wherein said steaming time ranges between 1 second and 10 minutes.

5. The method according to claim 1 wherein the time required to cool said steamed soybeans quickly to a temperature not exceeding C. is a time not exceeding 15 minutes. 

2. The method according to claim 1, wherein the steaming is completed so that the rate of digestion of the soybeans becomes not less than 90 percent and the turbidity grade thereof is zero.
 3. The method according to claim 1 wherein said gauge pressure ranges between 2 kilograms per square centimeter and 15 kilograms per square centimeter.
 4. The method according to claim 1 wherein said steaming time ranges between 1 second and 10 minutes.
 5. The method according to claim 1 wherein the time required to cool said steamed soybeans quickly to a temperature not exceeding 100* C. is a time not exceeding 15 minutes. 